This project aims to increase understanding of the role of virus-specific cytotoxic T lymphocytes (CTL) in virus control in human immunodeficiency virus type 1 (HIV-1)-infected individuals. HIV-1 is the causative agent of AIDS. The development of prophylactic and therapeutic strategies urgently required to combat this ultimately fatal infection is hampered by the current lack of understanding of the natural correlates of antiviral protection. In the first aim of this project, the contribution made by HIV-1-specific CTL to control of viremia at early times post-infection will be investigated. In collaboration with Drs. Shaw and Hahn, HIV-1- specific CTL activity will be analyzed temporally in a group of HIV-1- infected individuals from whom, uniquely, cryopreserved peripheral blood lymphocytes are available from the acute viremic phase prior to seroconversion onwards. By comparing CTL activity to individual HIV-1 proteins (measured in 51Cr release assays) with levels of HIV-1-specific antibodies, plasma viremia/antigenemia and the clinical status of these patients (followed by Drs. Shaw and Hahn), it will be possible to determine whether HIV-1-specific CTL activity correlates with clearance of the initial viremia and the subsequent early control of virus replication. Preliminary studies have shown an association between the magnitude of the early antiviral CTL response and the efficiency of control of primary HIV- 1 infection: this will be confirmed and extended. Further, in the second aim of the project, the primary CTL response will be characterized at the clonal level in a subset of patients. The viral epitopes recognized by clones established at early times post infection will be mapped by constructing vaccinia virus recombinants expressing segments of protein from the patients autologous early HIV-1 isolates, using these to identify epitope- containing regions, then pinpointing the epitopic sequence using synthetic peptides. The heteroclonality of the T cell population mediating the early antiviral CTL response will also be assessed by examining the T cell receptor usage of the early CTL clones. Whether the number of viral epitopes recognized in the early CTL response and/or heteroclonality of responding T cells correlates with the length of time for which infectious viremia is contained following clearance of primal viremia and rate of disease progression in different patients will be investigated. Definition of the most protective type of early antiviral CTL response will have important implications for vaccine design, and give clues as to the mechanisms which may be involved in the ultimate failure of the immune system to control persisting virus. In the third aim of the project, the hypothesis that evolution of CTL escape virus variants is of importance in the process by which virus eventually overcomes immune control will be tested. Whether autologous virus variants with epitopic mutations which affect recognition by early CTL are selected with time post-infection and whether the antiviral CTL response, in turn, evolves to recognize these viral variants in vivo will be investigated. Understanding how HIV-1 escapes immune control will allow the design of strategies to prevent re- emergence of persisting virus.